This is a deep subject, and I don’t pretend to be an expert, but even what I know, there is a lot to it. Let me first say that with guitar speakers, there is a fairly wide variance in how “identical models: will sound. These are not high fidelity drivers that are going in high end speakers or high end powered monitors. In fact, they are not made to be “pure.” They are made to create both frequency responses that vary from “flat” and contribute color in the form of distortions created by cone breakup. Duh!, right?
So, if you delve much into speaker construction, you’ll quickly realize that two of the same speaker built to different impedance, won’t sound the same. A 16 ohm V30 doesn’t sound the same as an 8 ohm V30.
So you have to know all that before you can get into amp OT theory. In theory, an amp will sound it’s “best” when used at the highest impedance the OT is wound for. So IF it has an OT wound for 16/8/4, a 16 ohm cab would sound the best because the other taps are tapping off early and aren’t using the full OT capacity. But, if it’s only an 8 ohm OT, then 8 ohm cabs should sound best.
Problem with all that? If the 16 ohm speakers are different than the 8 ohm version of the same model, how the heck do you know which actually sounds better? You can’t, without experimenting.
(Les Mode). “But DTR, why does tonemeister Brad Paisley only play on 16 ohms? Why do some vintage Marshall guys swear the same thing, that 16 ohms sound best?”
(Les mode off). Depends on the amp, and the cab. If the amp is designed with a 16 ohm OT, and the amp designer designed the amp around that company’s 16 ohm cab model, then chances are good that is the best match.
The moral of this story? When a really good amp designer designs an amp and cab together, buying the matching cab is often, but not always, your best bet.
Edit: This is the tip of the iceberg... I’m sure you’re bored already anyway, since you’re going to Experience, so I’ll stop here.